The present invention relates to image forming apparatuses, such as a laser printer, a digital copier, etc., which generate a color image.
In a general conventional image forming apparatus a laser beam, representing a predetermined image, is reflected on a rotating polygon mirror and then radiated to a rotating photosensitive body to form a latent image thereon. The photosensitive body is then charged with electricity, and the latent image thereon is developed and transferred onto a piece of recording paper via a transfer charger. The above process is repeated for each image color, and thus each image color is superimposed on the paper. Hereupon, the photosensitive body rotates indifferent to the input of the laser beam transmitted to it from the rotating polygon mirror, and to properly form the latent image on the photosensitive body, it is desirable to synchronize the rotation of the photosensitive body with the input of the laser beam transmitted thereto. However, an image forming apparatus having such a synchronizer shown in Japanese Laid-Open Patent Application No.57-19764 has a complicated circuitry construction and is expensive. On the other hand, without such a synchronizer, the rotation of the photosensitive body cannot be completely synchronous with the input of the laser beam and the image colors cannot be completely superimposed on each other. Thus, the image colors are shifted with respect to each other by at worst one dot, even if a recording timing of the laser beam, at which timing the laser beam is radiated on the photosensitive body, is controlled based on a position signal of the photosensitive body. In addition, a dot position of an end of a line cannot be always constant